The present invention is directed to a nanomechanical device, and more particularly to a nanomechanical device comprising self-assembled nanobimorphs for use as actuators, oscillators and sensors.
This invention relates in general to nanomechanical devices comprising motion controllable self-assembled nanobimorphs, and in particular to self-assembled carbon nanobimorphs used as mechanical elements such as actuators and oscillators, or force detectors with single molecule sensitivity comprising a self-assembled carbon nanobimorph comprising at least two nanofeatures such as nanotubes arranged separately on a pair of electrodes for applying a potential across the bimorph for either measuring the characteristic motion of, or creating a characteristic motion in the nanobimorph.
Nanoscale structures are becoming increasingly important because they provide the basis for devices with dramatically reduced power and mass and enhanced capabilities. Practical nanotechnology-based applications will require nanoscale sensors and actuators for characterization and manipulation on the molecular scale. In addition, nanoscale elements that move will be essential for interfacing between the macro and nano-worlds: for fabrication of nanoscale structures, for characterization of those structures, and for coupling real-world inputs and outputs to molecular-scale electronics.
Nanoscale mechanical structures would also enable the fabrication of high-quality-factor (Q) mechanical resonators with high mechanical responsivity. Such devices can form very low-loss, low-phase-noise oscillators for filters, local oscillators, and other signal processing applications. High-Q resonators are critical components in communications and radar systems, as well as in MEMS-based sensors such as a micro-gyroscope. The combination of high-Q with small force constants enabled by nanoscale resonators would also produce oscillators with exceptional force sensitivity. This sensitivity is important for a variety of force-detection-based sensors and may ultimately allow single molecule spectroscopy by NMR and optical techniques.
Nanoscale actuators and oscillators are also key components of mechanical signal processing systems. For example, actuators can be used to produce switches and mechanical transistors, while oscillator arrays containing elements with controllably varying resonant frequencies form the basis for high-speed Fourier analysis, similar to the frequency-dependent signal processing done in biological hearing systems. Mechanical signal processing is of great interest because small-scale, high-Q mechanical elements may theoretically enable processing at GHz rates with orders-of-magnitude lower power dissipation than conventional CMOS processors.
The emerging carbon nanotube technology offers exciting possibilities for producing useful nanoscale actuators and mechanical oscillators. Probing and manipulating on the molecular scale will require tools of a similar size. Carbon nanotubes provide a unique bridge between the macroscopic and nano-worlds because they have nanometer cross-sectional dimensions combined with tube lengths that can reach fractions of a millimeter. Nanotubes are well suited for use as robust, high-Q oscillators, because they possess near perfect molecular bonding coupled with extremely high tensile strength, and they exhibit elastic deformation even at high bending angles.
Despite the potential for these nanomechanical devices, the practical application of nanotube-based actuators and oscillators has been limited by the development of growth and processing methods for control of nanotube placement and orientation. These techniques are critical for a wide variety of other nanotube applications including nanotube electronic systems.
One novel approach to making nanometer-scale structures utilizes self-assembly of atoms and molecules to build up functional structures. In self-assembled processing, atom positions are determined by fundamental physical constraints such as bond lengths and angles, as well as atom-to-atom interactions with other atoms in the vicinity of the site being occupied. Essentially, self-assembly uses the principles of synthetic chemistry and biology to Agrow@ complex structures from a set of basic feedstocks. Utilizing such techniques molecular motors have been synthetically produced containing fewer than 80 atoms. Chemical vapor deposition (CVD) appears to be the most suitable method for nanotube production for sensor and electronic applications. CVD uses a carbon-containing gas such as methane, which is decomposed at a hot substrate surface (typically 600-900 C) coated with a thin catalyst film such as Ni or Co. However, most studies to date have produced disordered nanotube films.
A notable exception is the work of Prof. Xu who has developed a new technique for producing geometrically regular nanotube arrays with excellent uniformity in nanopore templates. Xu et al. Appl. Phys. Lett., 75, 367 (1999), incorporated herein by reference. Post-patterning of these ordered arrays could be used to selectively remove tubes in certain areas or produce regions with different length tubes. A variety of other studies have shown that dense, but locally disordered arrays of normally-oriented nanotubes can be selectively grown on pre-patterned catalyst layers. However, none of the current techniques have been able to grow vertical individual nanotubes or small groups of nanotubes with integrated electrodes, as would be necessary to form nanotube oscillators or actuators.
In addition, there has been little progress in the control of nanotube orientation in the plane parallel to the substrate surface. Many of the basic electrical measurements of nanotubes have been done using electrodes placed on randomly scattered tubes after growth, or by physically manipulating tubes into place with an atomic force microscope (AFM). Dai and co-workers have been able to demonstrate random in-plane growth between closely spaced catalyst pads, including growth over trenches, as well as a related technique to produce nanotubes suspended between Si posts. Dai. Et al., Science, 283, 512 (1999), incorporated herein by reference. In these cases individual nanotubes sometimes contact adjacent electrodes by chance, and excess tubes can be removed with an AFM tip. This type of procedure can be effective for simple electrical measurements, but considerable improvements will be required for production of more complex nanotube circuits. Smalley""s group has demonstrated a wet chemistry-based method of control over nanotube placement using solution deposition on chemically functionalized substrates, although questions remain about nanotube length control and contact resistance. Smalley et al., Nature, 391, 59 (1998), incorporated herein by reference. However, none of the current techniques have been able to grow vertical individual nanotubes or small groups of nanotubes with integrated electrodes, as would be necessary to form nanotube oscillators or actuators.
In addition to the problems associated with controlled growth and orientation of nanotubes, nanotube actuators and oscillators also require a transduction mechanism to convert input signals to physical motion and to provide corresponding output signals.
One possible mechanism is suggested by a recent demonstration that nanotube mats can serve as very high efficiency electromechanical actuators in an electrolyte solution, with the possibility of even better results for well-ordered single wall tubes. Baughman et al., Science, 284 1340 (1999), incorporated herein by reference. Other potential actuation mechanisms to be investigated include light-induced nanotube motion, which has been observed, and magnetomotive actuation. However, these techniques have only been demonstrated for large disordered arrays of nanotubes, no technique has been developed for the controlled motion of individual nanotube bimorphs
Accordingly, a need exists to develop nanoscale mechanical devices, such as, actuators and oscillators to enable applications ranging from molecular-scale characterization and manipulation, to ultra-low-loss mechanical filters and local oscillators for communications and radar, to rad-hard low-power mechanical signal processors.
The present invention is directed to a nanomechanical device and system utilizing nanobimorphs comprising at least two adjacent nanofeatures, such as nanotubes, in a touching relation at one end, and means for inducing a difference in charge density between the tubes (e.g. by biasing one tube positive with respect to the other with sufficient tube-to-tube contact resistance) such that lateral movement is induced in the end of the bimorph, forming a nanoscale actuator, as well as a force sensor when operated in an inverse mode. The invention is also directed to growth techniques capable of producing a novel nanotube bimorph structure with integrated electrodes.
In one embodiment this invention utilizes a nanobimorph with an integrated electrode substrate that functions as an oscillator or actuator. This invention is also directed to a device which utilizes a nanobimorph with an integrated electrode substrate that functions as a molecular sensor. This invention is also directed to novel systems and methods for utilizing devices comprising at least one nanobimorph with an integrated electrode substrate.
In another embodiment, the invention is directed to a nanobimorph actuator comprising a nanobimorph with an integrated electrode substrate. The nanoscale actuators of the present invention are designed to provide the capability of controllable motion on near-atomic scales. In such an embodiment, the transduction mechanism is symmetricxe2x80x94length changes in the nanotubes will induce charge transfer and hence voltages, providing a readout mechanism for the actuators.
In another alternative embodiment, the induced voltage is produced by optical irradiation.
In still another embodiment, the invention is directed to nanobimorph oscillators or resonators. The nanobimorph oscillators may be utilized as high-Q mechanical resonators for filters, signal processing, and sensors. In such an embodiment, excitation and readout of a nanobimorph oscillator may be made using the actuation methods previously discussed in the nanobimorph actuator section: piezoelectric, light, or electrostatic.
In yet another embodiment, the invention is directed to mechanical signal processing systems utilizing the nanobimorph actuators and oscillators of the current invention. For example, in one embodiment, actuators can be used to produce switches and mechanical transistors, while in another embodiment oscillator arrays containing elements with controllably varying resonant frequencies form the basis for high-speed Fourier signal processing.
In still yet another embodiment the nanotubes comprising the nanobimorph self-assemble into the nanobimorph having a specified diameter and height suitable for use in the devices of the current invention.
In still yet another embodiment, the substrate is made of a semiconductor such as, for example, oxidized silicon or aluminum oxide, coated with a metal catalyst film such as, for example, Ni or Co. In this embodiment, the silicon can be further doped to adjust the electronic properties of the substrate surface.
In still yet another embodiment, the nanotubes comprising the nanobimorph are self-assembled from an inert material such as, for example, carbon utilizing a carbon feedstock gas such as, for example, ethylene.
In still yet another embodiment, the invention is directed to a system for the detection of substances comprising multiple detectors as described above, such that parallel processing of molecules can be carried out.
In still yet another embodiment, the invention is directed to growth and processing techniques to control nanobimorph location and orientation; and methods for positioning nanotubes during growth, including nanoscale patterning of catalyst dots to seed the growth of vertical nanotubes on integrated electrodes.